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    <title>Math.sin(x) 返回角度 x（以弧度计）的正弦</title>
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    <h1>JavaScript Math.sin()</h1>
    <p>Math.sin(x) 返回 x（以弧度计）的正弦：</p>
    <p>以弧度计的角度 = (以度数计的角度) * PI / 180。</p>
    <p id="demo"></p>
    <script>
        document.getElementById("demo").innerHTML = "The sine value of 90 degrees is " + Math.sin(90 * Math.PI / 180);
    </script>
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